识别 data.table 中行之间的差异并创建新列，说明差异是什么答案

【问题标题】：Identify the difference between rows in data.table and create new column saying what the differences are识别 data.table 中行之间的差异并创建新列，说明差异是什么
【发布时间】：2019-02-03 10:08:04
【问题描述】：

我有一个如下所示的数据集：

Data01 <- data.table(
  code=c("A111", "A111","A111","A111","A111", "A111","A111","A234", "A234","A234","A234","A234", "A234","A234"),
  x=c("",126,126,"",836,843,843,126,126,"",127,836,843,843), 
  y=c("",76,76,"",456,465,465,76,76,"",77,456,465,465),
  no1=c(028756, 028756,028756,057756, 057756, 057756, 057756,028756, 028756,057756,057756, 057756, 057756, 057756),
  no2=c("","",034756,"","","",789165,"",034756,"","","","",789165)
)

Data01[, version := paste0("V", 1:.N), by = code]
Data01[, unique_version := paste(code, version, sep = "_")]

我想要的是一种为每个唯一的code 条目添加一列的方法，该列说明每一行与前一行之间的区别是什么（即，将列名粘贴到现在有不同值的地方） .像这样的：

Data01[, change := c("First_entry","New_x_and_y","New_no2","New_x_and_y_and_no_1","New_x_and_y","New_x_and_y","New_no2","First_entry","New_no2","New_x_and_y_and_no1","New_x_and_y","New_x_and_y","New_x_and_y","New_no2")]

我的实际数据集有 550 万行和大约 260 万个唯一的 code 条目，所以我想任何解决方案都需要一些时间才能完成。因此，如果可能的话，包含某种进度指示器（如此处建议的内容：Progress bar in data.table aggregate action）将非常有帮助。

【问题讨论】：

标签： r data.table

【解决方案1】：

你可以试试这样的

nm <- c("x","y","no1","no2") #names(Data01)[-1L]
Data01[, change := c("First_entry", 
        sapply(seq_len(.N)[-1L], function(n) {
            paste(c("New", 
                nm[which(unlist(.SD[n-1L]) != unlist(.SD[n]))]), 
                collapse="_")
        })), 
    by=.(code)]

【讨论】：